CN116971769A - Method for predicting extension direction of hydraulic fracture of conglomerate - Google Patents
Method for predicting extension direction of hydraulic fracture of conglomerate Download PDFInfo
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B49/00—Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/25—Methods for stimulating production
- E21B43/26—Methods for stimulating production by forming crevices or fractures
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B2200/00—Special features related to earth drilling for obtaining oil, gas or water
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Abstract
The invention discloses a method for predicting the expansion direction of a hydraulic fracture of a conglomerate, which comprises the following steps: obtaining geological parameters and fracturing construction parameters; generating a geometric model containing gravels through the shape and the direction of the gravels, the position distribution of the gravels in the space, the particle size of the gravels and the content of the gravels; assigning parameters of the matrix and the gravel respectively; establishing a rock deformation model for the expansion of the fracturing cracks; establishing a fluid flow model of fracture propagation; establishing a hydraulic fracture and gravel intersection action criterion; the influence rule of the gravel on the hydraulic fracture expansion is explored by changing the size and the content of the gravel. The invention establishes the intersecting action rule of the hydraulic fracture and the gravel based on the two-dimensional displacement discontinuous method, can accurately simulate the complex track after the hydraulic fracture and the gravel are intersected, and is beneficial to revealing the interaction mechanism of the hydraulic fracture and the gravel.
Description
Technical Field
The invention relates to a method for predicting the expansion direction of a hydraulic fracture of a conglomerate, and belongs to the field of oil and gas field yield increase transformation.
Background
The volume fracturing of the horizontal well becomes a main development mode of unconventional dense oil reservoirs such as Xinjiang Mahu conglomerate oil reservoirs, and the like, accurately simulates a crack extension rule under the influence of gravels, and is important to meet domestic oil gas resources and ensure national energy safety.
The conglomerate reservoir has the characteristics of strong heterogeneity, poor basic physical properties, low pore, low permeability, various pore types, complex pore structures and the like, and conventional hydraulic fracturing cannot obtain effective industrial productivity, so that a horizontal well volume fracturing technology is required, which is very mature in shale reservoir development, but the conglomerate reservoir has a certain influence on hydraulic fracture extension tracks due to the existence of gravels. Therefore, the influence rule of the gravel on the hydraulic fracture needs to be explored, and the characterization of the gravel in the stratum is also particularly critical, and generally comprises the shape, the azimuth, the position distribution, the particle size and the content of the gravel. After the hydraulic fracture is intersected with the gravel, various complex interaction results are generated, namely various complex fracturing fracture characteristics such as gravel stopping, gravel penetrating, gravel winding and the like appear, and a set of relatively perfect fracture expansion judgment criteria is not established at present.
Disclosure of Invention
The invention provides a method for predicting the hydraulic fracture propagation direction of a conglomerate in order to overcome the defect that a set of perfect fracture propagation judging criteria is not formed in the prior art.
The technical scheme provided by the invention for solving the technical problems is as follows: a method for predicting the extension direction of a hydraulic fracture of a conglomerate comprises the following steps:
step 1: obtaining geological parameters and fracturing construction parameters;
step 2: generating a geometric model containing gravels through the shape and the direction of the gravels, the position distribution of the gravels in the space, the particle size of the gravels and the content of the gravels;
step 3: assigning parameters of the matrix and the gravel respectively;
step 4: establishing a rock deformation model for the expansion of the fracturing cracks;
step 5: establishing a fluid flow model of fracture propagation;
step 6: establishing a hydraulic fracture and gravel intersection action criterion;
step 7: the influence rule of the gravel on the hydraulic fracture expansion is explored by changing the size and the content of the gravel.
The geological parameters of the step 1 comprise reservoir thickness, gravel shape and orientation, gravel space position distribution, gravel particle size, gravel content, horizontal maximum principal stress, horizontal minimum principal stress, young's modulus, poisson's ratio, matrix and gravel fracture toughness, and cementing surface fracture toughness. The fracturing construction parameters include injection rate, fracturing fluid viscosity and fracturing fluid density.
The gravel shape and orientation of the step 2 are characterized by adopting irregular polygons, and in a polar coordinate system, the shape of the polygon is determined by the number m of vertexes and the polar angle theta i Polar radius R i Expressed as:
θ i =η 1 ×2π (1)
R i =A 0 +(2η i -1)×A 1 (2)
wherein: η (eta) 1 A random number between 0 and 1; a is that 0 Is of radius R i Average value of (d), mm; a is that 1 Is of radius R i Increased value of (2) mm; η (eta) i Is a random number between 0 and 1.
The gravel space position distribution can be expressed as:
wherein: w (W) min The minimum value of the abscissa of the research area is m; w (W) max Study area abscissa maximum, m; h min The minimum value of the ordinate of the research area is m; h max Study area ordinate maximum, m; lambda (lambda) 1 ,λ 2 Is a random number between 0 and 1.
The probability density function of the gravel particle size distribution is expressed as:
wherein: l (L) a Is the size of the long axis, mm; u is the average value of the major axis size of the gravel, and mm; sigma is the variance of the major axis size of the gravel, mm 2 。
The gravel content can be expressed as:
wherein: η is the gravel content in the investigation region,%; m is the number of gravels in the investigation region; s is S i Is the area of the ith gravel, m 2 The method comprises the steps of carrying out a first treatment on the surface of the S is the total area of the investigation region, m 2 。
The further technical scheme is that the rock deformation model of the fracturing crack extension in the step 4 is as follows:
wherein: sigma (sigma) n,i ,σ s,i The normal stress and the tangential stress of the crack unit i are respectively applied to MPa; n represents the total number of crack units; b represents a boundary strain influence coefficient matrix; d (D) s,j Representing the tangential displacement discontinuity at the fracture cell j; d (D) n,j Representing the amount of normal displacement discontinuity at the fracture cell j.
The further technical scheme is that the fluid flow model of the fracturing fracture expansion in the step 5 is as follows:
wherein: q (s, t) is the flow of the section s at the current moment, m 3 /min;q t (s, t) is the fracturing fluid filtration rate, m of the unit joint length of the s section at the current moment 2 A/min; a (s, t) the sectional area of the s-section crack at the current moment, m 2 The method comprises the steps of carrying out a first treatment on the surface of the t is the fracturing construction time length, min; p is the fluid friction in the hydraulic fracture; n represents the water power law index; k represents a fluid viscosity index; h is the thickness of the reservoir, m; w represents the width of the hydraulic fracture, m; c (C) t Is the fluid loss coefficient of fracturing fluid, m/min 0.5 ;t 0 The crack opening time, min.
A further technical scheme is that the hydraulic fracture and the gravel in the step 6 are intersected.
The criteria for hydraulic fracture gravel stopping can be expressed as:
K e <min(K IC_C ,K IC_G ) (10)
wherein: k (K) e Is equivalent stress intensity factor of crack tip and MPa.m 0.5 ;K IC_C As critical fracture toughness of cementing surface between matrix and gravel, MPa.m 0.5 ;K IC_G Critical fracture toughness of gravel, MPa.m 0.5 。
The criteria for determining the hydraulic fracture passing through the gravel can be expressed as:
wherein: k (K) v1 ,K v2 The virtual equivalent stress intensity factor representing that the hydraulic fracture is relatively easy and relatively difficult to spread along the cementing surface between the matrix and the gravel is calculated as follows:
wherein:is the approximation of the intersection of a hydraulic fracture with gravelAngle, degree.
The occurrence of gravel winding can be divided into 4 types, and the judgment criterion of unidirectional gravel winding of the hydraulic fracture along the cementing surface between the matrix and the gravel can be expressed as follows:
the criteria for determining the bidirectional detritus of the hydraulic fracture along the cementing surface between the matrix and the gravel can be expressed as:
the judgment criteria of the unidirectional deviation or bidirectional deviation behavior of the hydraulic fracture when the hydraulic fracture extends along the cementing surface are as follows:
wherein: k (K) v0 Is the virtual equivalent stress intensity factor of the hydraulic fracture along the expansion direction of the current cementing surface, namelyMPa·m 0.5 。
If the above-described migration conditions are not met, the hydraulic fracture may continue along the cementing surface or to the end point of the cementing surface, turning further into the matrix rock.
According to a further technical scheme, the step 7 is used for changing the size of the gravel and the influence rule of the gravel content on the expansion of the hydraulic fracture, and comparing the extension tracks of the hydraulic fracture with different sizes of the gravel and different gravel contents, so that the interaction mechanism of the hydraulic fracture and the gravel is revealed.
The invention has the following beneficial effects: the invention fully considers the shape, the direction, the position distribution, the particle size and the content of the gravels, and establishes a complete crack extension judgment criterion which is helpful for revealing the interaction mechanism of the hydraulic crack and the gravels.
Drawings
FIG. 1 is a schematic diagram of a geometric model containing conglomerates
FIG. 2 is a schematic illustration of hydraulic fracture and gravel interaction process
FIG. 3 is a graph comparing hydraulic fracture propagation trajectories with different gravel contents
FIG. 4 is a graph showing the comparison of hydraulic fracture propagation trajectories with different gravel particle sizes
Detailed Description
The invention will be further described with reference to examples and figures.
The method for predicting the extension direction of the hydraulic fracture of the conglomerate can accurately and rapidly calculate the shape and the distribution of the gravel, can simulate various complex interaction results generated after the hydraulic fracture is intersected with the gravel, and mainly comprises the following steps:
step 1: obtaining geological parameters and fracturing construction parameters;
wherein the geological parameters include reservoir thickness, gravel shape and orientation, gravel spatial location distribution, gravel particle size, gravel content, horizontal maximum principal stress, horizontal minimum principal stress, young's modulus, poisson's ratio, matrix and gravel fracture toughness, and cement face fracture toughness. The fracturing construction parameters include injection rate, fracturing fluid viscosity and fracturing fluid density.
Step 2: generating a geometric model containing gravels through the shape and the direction of the gravels, the position distribution of the gravels in the space, the particle size of the gravels and the content of the gravels;
wherein the gravel shape and orientation are characterized by irregular polygons, and in a polar coordinate system, the shape of the polygon is determined by the number m of vertexes and the polar angle theta i Polar radius R i Expressed as:
θ i =η 1 ×2π (1)
R i =A 0 +(2η i -1)×A 1 (2)
wherein eta is 1 A random number between 0 and 1; a is that 0 Is of radius R i Average value of (mm);A 1 Is of radius R i Increased value of (2) mm; η (eta) i Is a random number between 0 and 1.
The gravel space position distribution can be expressed as:
wherein: w (W) min The minimum value of the abscissa of the research area is m; w (W) max Study area abscissa maximum, m; h min The minimum value of the ordinate of the research area is m; h max Study area ordinate maximum, m; lambda (lambda) 1 ,λ 2 Is a random number between 0 and 1.
The probability density function of the gravel particle size distribution is expressed as:
wherein: l (L) a Is the size of the long axis, mm; u is the average value of the major axis size of the gravel, and mm; sigma is the variance of the major axis size of the gravel, mm 2 。
The gravel content can be expressed as:
wherein: η is the gravel content in the investigation region,%; m is the number of gravels in the investigation region; s is S i Area of ith gravel, mm 2 The method comprises the steps of carrying out a first treatment on the surface of the S is the total area of the investigation region, mm 2 。
Thereby obtaining the geometric model containing the conglomerate.
Step 3: assigning parameters of the matrix and the gravel respectively;
wherein the basic parameters relating to matrix and gravel in step 1 are assigned to the conglomerate-containing model.
Step 4: establishing a rock deformation model for the expansion of the fracturing cracks;
rock deformation model in which fracture propagation:
wherein: sigma (sigma) n,i ,σ s,i The normal stress and the tangential stress of the crack unit i are respectively applied to MPa; n represents the total number of crack units; b represents a boundary strain influence coefficient matrix; d (D) s,j Representing the tangential displacement discontinuity at the fracture cell j; d (D) n,j Representing the amount of normal displacement discontinuity at the fracture cell j.
Step 5: establishing a fluid flow model of fracture propagation;
the fluid flow model in which the fracture propagates is:
wherein: q (s, t) is the flow of the section s at the current moment, m 3 /min;q t (s, t) is the fracturing fluid filtration rate, m of the unit joint length of the s section at the current moment 2 A/min; a (s, t) the sectional area of the s-section crack at the current moment, m 2 The method comprises the steps of carrying out a first treatment on the surface of the t is the fracturing construction time length, min; p is the fluid friction in the hydraulic fracture; n represents the water power law index; k represents a fluid viscosity index; h is the thickness of the reservoir, m; w represents the width of the hydraulic fracture, m; c (C) t Is the fluid loss coefficient of fracturing fluid, m/min 0.5 ;t 0 The crack opening time, min.
Step 6: establishing a hydraulic fracture and gravel intersection action criterion;
the judgment criterion of hydraulic fracture gravel stopping can be expressed as follows:
K e <min(K IC_C ,K IC_G ) (10)
wherein K is e Is equivalent stress intensity factor of crack tip and MPa.m 0.5 ;K IC_C As critical fracture toughness of cementing surface between matrix and gravel, MPa.m 0.5 ;K IC_G Critical fracture toughness of gravel, MPa.m 0.5 。
The criteria for determining the hydraulic fracture passing through the gravel can be expressed as:
wherein K is v1 ,K v2 The virtual equivalent stress intensity factor representing that the hydraulic fracture is relatively easy and relatively difficult to spread along the cementing surface between the matrix and the gravel is calculated as follows:
wherein:is the angle of approach, in degrees, of the hydraulic fracture when it intersects the gravel.
The occurrence of gravel winding can be divided into 4 types, and the judgment criterion of unidirectional gravel winding of the hydraulic fracture along the cementing surface between the matrix and the gravel can be expressed as follows:
the criteria for determining the bidirectional detritus of the hydraulic fracture along the cementing surface between the matrix and the gravel can be expressed as:
the judgment criteria of the unidirectional deviation or bidirectional deviation behavior of the hydraulic fracture when the hydraulic fracture extends along the cementing surface are as follows:
wherein: k (K) v0 Is the virtual equivalent stress intensity factor of the hydraulic fracture along the expansion direction of the current cementing surface, namelyMPa·m 0.5 。
If the above-described migration conditions are not met, the hydraulic fracture may continue along the cementing surface or to the end point of the cementing surface, turning further into the matrix rock.
Step 7: the influence rule of the gravel on the hydraulic fracture expansion is explored by changing the size and the content of the gravel.
The method comprises the steps of changing the size and the content of the gravel, exploring the influence rule of the geometric model of the gravel-containing water conservancy cracks by changing the parameters of the gravel, and comparing the extension tracks of the water conservancy cracks with different sizes and contents of the gravel, so that the interaction mechanism of the water conservancy cracks and the gravel is revealed.
Examples:
step 1: the geological and fracturing construction parameters of the present invention are shown in table 1.
TABLE 1 basic parameter Table for calculation of conglomerate formation
Step 2: the size of the model is set to be 0.1m multiplied by 0.4m, the injection point is positioned at the center of the model, the size of the randomly distributed gravels is 10-12 mm, the shape of the gravels is heptagon, the gravel content is 40%, and the geometric model of the conglomerate is shown in figure 1.
Step 3: parameters of the substrate and gravel are assigned separately.
Step 4-6: the parameters of table 1 were taken into the set of equations established by the present invention for simulation, and a schematic diagram of the hydraulic fracture and gravel interaction process is shown in fig. 2.
Step 7: calculation example 1: the law of influence of different gravel contents on hydraulic fracture propagation is explored. The gravel size was set to 10-12 mm, the gravel content was 20%, 40% and 60%, respectively, and the remaining parameters were kept consistent with table 1. The simulation results are shown in fig. 3. As the gravel content increases, the interaction of the hydraulic fracture with the gravel dominates. When the gravel content is low, the hydraulic fracture shape is relatively flat, and the local occurrence of detritus is accompanied by the passing and stopping of the detritus. When the gravel content increases to 60%, the hydraulic fracture predominates around the gravel, causing the hydraulic fracture to become more tortuous.
Calculation example 2 explores the influence rule of different gravel particle sizes on hydraulic fracture propagation, and the average particle sizes of the gravels are set to be 6.6mm, 13.2mm and 22.0mm respectively, and the rest parameters are consistent with Table 1. The simulation results are shown in fig. 4. As the gravel size increases, the hydraulic fracture continues to grow predominantly around the gravel, with the attendant penetration, stopping and bifurcation. However, when the particle size of the gravels is smaller, the number of the distributed gravels is larger, the interaction between the hydraulic fracture and the gravels is more, a small amount of gravels penetrate and stop the gravels, so that the fracture track is bent and complicated, and when the particle size of the gravels is larger, the number of the distributed gravels is smaller, the hydraulic fracture has enough free expansion space, so that the whole hydraulic fracture is relatively flat, and only the local fracture track is relatively bent.
The present invention is not limited to the above-mentioned embodiments, but is not limited to the above-mentioned embodiments, and any person skilled in the art can make some changes or modifications to the equivalent embodiments without departing from the scope of the technical solution of the present invention, but any simple modification, equivalent changes and modifications to the above-mentioned embodiments according to the technical substance of the present invention are still within the scope of the technical solution of the present invention.
Claims (3)
1. The method for predicting the extension direction of the hydraulic fracture of the conglomerate is characterized by comprising the following steps of:
step 1: obtaining geological parameters and fracturing construction parameters;
step 2: generating a geometric model containing gravels through the shape and the direction of the gravels, the position distribution of the gravels in the space, the particle size of the gravels and the content of the gravels;
step 3: assigning parameters of the matrix and the gravel respectively;
step 4: establishing a rock deformation model for the expansion of the fracturing cracks;
step 5: establishing a fluid flow model of fracture propagation;
step 6: establishing a hydraulic fracture and gravel intersection action criterion;
step 7: the influence rule of the gravel on the hydraulic fracture expansion is explored by changing the size and the content of the gravel.
2. The method for predicting the hydraulic fracture propagation direction of the conglomerate according to claim 1, wherein the specific process of the step 2 is as follows:
in a polar coordinate system, determining the shape of a polygon from the number of vertices m, polar angle θ i Polar radius R i Expressed as:
θ i =η 1 ×2π (1)
R i =A 0 +(2η i -1)×A 1 (2)
wherein: η (eta) 1 A random number between 0 and 1; a is that 0 Is of radius R i Average value of (d), mm; a is that 1 Is of radius R i Increased value of (2) mm; η (eta) i A random number between 0 and 1;
the gravel space position distribution can be expressed as:
wherein: w (W) min The minimum value of the abscissa of the research area is m; w (W) max Study area abscissa maximum, m; h min The minimum value of the ordinate of the research area is m; h max Study area ordinate maximum, m; lambda (lambda) 1 ,λ 2 A random number between 0 and 1;
the probability density function of the gravel particle size distribution is expressed as:
wherein: l (L) a Is the size of the long axis, mm; u is the average value of the major axis size of the gravel, and mm; sigma is the variance of the major axis size of the gravel, mm 2 ;
The gravel content can be expressed as:
wherein: η is the gravel content in the investigation region,%; m is the number of gravels in the investigation region; s is S i Area of ith gravel, mm 2 The method comprises the steps of carrying out a first treatment on the surface of the S is the total area of the investigation region, mm 2 。
3. The method for predicting the propagation direction of a hydraulic fracture of a conglomerate according to claim 1, wherein the specific hydraulic fracture and gravel crossing action criteria are as follows:
the criteria for hydraulic fracture gravel stopping can be expressed as:
K e <min(K IC_C ,K IC_G ) (10)
wherein: k (K) e Is equivalent stress intensity factor of crack tip and MPa.m 0.5 ;K IC_C As critical fracture toughness of cementing surface between matrix and gravel, MPa.m 0.5 ;K IC_G Critical fracture toughness of gravel, MPa.m 0.5 ;
The criteria for determining the hydraulic fracture passing through the gravel can be expressed as:
wherein: k (K) v1 ,K v2 The virtual equivalent stress intensity factor representing that the hydraulic fracture is relatively easy and relatively difficult to spread along the cementing surface between the matrix and the gravel is calculated as follows:
wherein:an approximation angle, DEG, when the hydraulic fracture intersects the gravel;
the occurrence of gravel winding can be divided into 4 types, and the judgment criterion of unidirectional gravel winding of the hydraulic fracture along the cementing surface between the matrix and the gravel can be expressed as follows:
the criteria for determining the bidirectional detritus of the hydraulic fracture along the cementing surface between the matrix and the gravel can be expressed as:
the judgment criteria of the unidirectional deviation or bidirectional deviation behavior of the hydraulic fracture when the hydraulic fracture extends along the cementing surface are as follows:
wherein: k (K) v0 Is the virtual equivalent stress intensity factor of the hydraulic fracture along the expansion direction of the current cementing surface, namelyMPa·m 0.5 ;
If the above-described migration conditions are not met, the hydraulic fracture may continue along the cementing surface or to the end point of the cementing surface, turning further into the matrix rock.
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CN114372428A (en) * | 2022-01-13 | 2022-04-19 | 西南石油大学 | Extension and trans-scale simulation method for multiple clusters of fracturing fractures in horizontal well section of glutenite reservoir |
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Publication number | Priority date | Publication date | Assignee | Title |
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CN114372428A (en) * | 2022-01-13 | 2022-04-19 | 西南石油大学 | Extension and trans-scale simulation method for multiple clusters of fracturing fractures in horizontal well section of glutenite reservoir |
CN114372428B (en) * | 2022-01-13 | 2024-04-12 | 西南石油大学 | Multi-cluster fracturing crack extension trans-scale simulation method in horizontal well section of sandstone reservoir |
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